1. Field of the Invention
The present invention relates generally to circuit breakers and, more particularly, to a circuit breaker having a delay mechanism that slightly delays the actuation of a switch upon moving the circuit breaker from an OFF condition to an ON condition.
2. Description of the Related Art
Circuit breakers and other power distribution equipment are generally known. A power distribution system often includes circuit breakers in a cascaded configuration that provides coordinated operation such that upon the occurrence of a fault condition or other condition requiring an interruption of power the circuit breaker in the closest upstream location trips. Such a system is provided in order to limit the power interruption in other areas that are unaffected by the fault or other condition.
Sometimes a given circuit breaker in a power distribution system is in an OFF condition while other circuit breakers in the power distribution system are in an ON condition. If a fault condition arises upon switching the OFF circuit breaker to an ON condition, such as when the circuit breaker closes onto a fault, it would be most desirable to trip the circuit breaker that was most recently switched to an ON condition. Circuit breakers in a power distribution system thus often are electronically connected together in order to enable in such a circumstance immediate tripping of the circuit breaker that was most recently switched to an ON condition. To enable such an electronic interconnection, the circuit breakers typically each include a trip unit that is configured to detect a change in condition of the circuit breaker, i.e., from an OFF condition to an ON condition.
Trip units of this type typically can be either externally powered, i.e., being powered by an auxiliary power system, or can be self-powered, i.e., by employing current transformers to draw current directly from the protected circuit. Self-powered trip units have had a particular shortcoming in that the electronics thereof do not become fully operational until a brief period of time after the circuit breaker has been switched to an ON condition. Specifically, upon switching the circuit breaker to an ON condition, current flows through the circuit breaker conductors, and the current transformers draw some of the current to begin powering the electronics. The electronics do not become operational until after the circuit breaker has been switched to an ON condition, and thus the self-powered trip unit cannot distinguish between a circumstance in which its associated circuit breaker had been in an ON condition but unpowered or if its associated circuit breaker was in an OFF condition and became powered by being switched to an ON condition.
It thus would be desirable to provide a circuit breaker having a self-powered trip unit that can distinguish between a first situation in which an unpowered circuit breaker in an ON condition became powered and a second situation in which a circuit breaker in an OFF condition became powered by switching it to an ON condition. Such a circuit breaker preferably would include an inertial delay mechanism that provides an appropriate time delay without requiring the use of a significant inertial mass.